The power-up in this level stays in the same place the whole time, and can be acquired at any time - the difficulty is that this is a very large, open, and distracting map. Although it is sitting at a fixed point in space, the planet below you combined with the battle above you and the background with additional ships, stars, and other images simply make it hard to find.

To find it at the beginning you can choose to fly straight from the starting position (don't move) and try and look for a glimmering spot diagonally downwards and to the left of the leftmost Star Destroyer (the power-up is at about the same distance from you as the Star Destroyer).

The easiest way, however, is to destroy the left Star Destroyer. Wait until it falls all the way and stops. While it's hanging there in space, fly down underneath it and find the white area that you could potentially fly into (the hangar). The upgrade will be inside the ship where you can't see it, but if you fly into the hangar you'll be within the distance needed to grab the power-up anyways - make sure you have sound on so you can confirm you received it.